Download Chapter 7 Chemical Formulas

Chapter
7
Chemical
Formulas
Chemical Formulas and Names
Subscripts: Indicate the number of each
atom in a formula
 Hydrocarbons: molecular compounds
composed of only carbon and hydrogen.
 Ex. Al2(SO4)3
*subscript 2 refers to 2 Al ions
*subscript 4 refers to 4 O atoms in the
sulfate ion
*subscript 3 refers to everything inside the
( ), giving us 3 sulfate ions, with a total of
3 sulfur atoms and 12 oxygen atoms

7-2
Chemical Formulas and Names
 Monatomic
Ions: ions formed from a
single atom
 Monatomic cations (+) are named
after the element. Ex. Sodium =
sodium
 Monatomic anions ( -), the end of
the element name is dropped and ide
is added. Ex. Chlorine = chloride
oxygen = oxide
7-3
Balancing Charges
Binary Compounds: compounds
composed of two elements
 The total positive and negative charges
must be equal
 Charges are balanced by having more
than one of an ion, which is indicated by a
subscript
 Ex. Magnesium Bromide = Mg+2 and Br -1
~ +2 and -1 are not balanced, you need
two of the bromines to balance the
charge: MgBr2

7-4
Balancing Charges
Ex. What is the formula for aluminum
oxide?
1.To write balanced ionic formulas, first
write the symbols for the ions side by
side, cations first: Al3+ O22. Cross over the charges by using the
absolute value of each ion’s charge as
the subscript for the other ion: Al23+ O3-2
3. Check the subscripts and simplify if
necessary. Final answer = Al2 O3
7-5
Practice
1)
Write balanced formulas for the following binary
ionic compounds:
a)
Sodium chloride:________________________
b)
Zinc Oxide:____________________________
c)
Aluminum Bromide:_____________________
a)
Barium Phosphide:______________________
7-6
Practice
1)
Write balanced formulas for the following binary
ionic compounds:
a)
Sodium
chloride:_____NaCl___________________
b)
Zinc Oxide:_________ZnO_______________
c)
Aluminum Bromide:______AlBr3__________
d)
Barium Phosphide:__Ba3P2________________
7-7
Naming Binary Compounds



Nomenclature: naming system
for chemicals
For binary ionic compounds,
name the cation first, then the
anion.
Ex. CaCl2 is calcium chloride.
7-8
Practice
a)
What are the names of the
following binary ionic compounds?
Sr3N2:___________________
b)
KI:______________________
c)
Li2S:____________________
2)
7-9
Practice
a)
What are the names of the
following binary ionic compounds?
Sr3N2: Strontium Nitride
b)
KI: Potassium Iodide
c)
Li2S: Lithium sulfide
2)
7-10
Naming Binary Compounds

Some metals form cations with
different charges, a roman numeral
is used in the name to indicate the
charge of the ion.
ex. Iron II = Fe+2 Iron III = Fe+3
ex. What is the formula for copper
II oxide? Cu+2 O-2 = Cu2O2 = CuO
7-11
Practice
3)
a)
b)
4)
a)
b)
What are the formulas for the
following binary ionic compounds?
Iron III sulfide:____________
Copper I oxide:____________
What are the names of the
following binary ionic compounds?
CrF2:_____________________
Pb3N4:____________________
7-12
Practice
3)
a)
b)
4)
a)
b)
What are the formulas for the
following binary ionic compounds?
Iron III sulfide:__Fe2S3______
Copper I oxide:___Cu2O______
What are the names of the
following binary ionic compounds?
CrF2:_____Chromium II Fluoride__
Pb3N4:_____Lead IV Nitride____
7-13
Polyatomic Ions


Polyatomic Ions: are made up of
more than one atom.
Oxyanions: polyatomic ions that
contain oxygen. (the name of the
ion with the greater number of O
atoms ends in ate, with lesser O
atoms is ite)
ex. NO2- = nitrite NO3- = nitrate
7-14
Writing Polyatomic Formulas

Charges are balanced just like in
binary compounds, but if you need
more than one of a polyatomic ion,
you must put it in parenthesis with
your subscript on the outside.
ex. What is the formula for
tin IV sulfate? Sn 4+ SO42- =
Sn(SO4)2
7-15
Practice
5)
a)
b)
c)
d)
e)
Write the formulas for the following
ionic compounds:
Sodium iodide:_____________
Lithium nitrate:_____________
Copper II sulfate:___________
Sodium Carbonate:__________
Potassium perchlorate:_______
7-16
Practice
5)
a)
b)
c)
d)
e)
Write the formulas for the following
ionic compounds:
Sodium iodide:____NaI_____
Lithium nitrate:____LiNO3_____
Copper II sulfate:__CuSO4_____
Sodium Carbonate:____Na2CO3___
Potassium perchlorate:__KClO4__
7-17
Practice
6)Write the names for the following
ionic compounds:
a) Ca(OH)2____________________
b) KClO3:______________________
c) NH4OH:_____________________
d) Fe2(CrO4)3:___________________
e) KClO:_______________________
7-18
Practice
6)Write the names for the following
ionic compounds:
a) Ca(OH)2:__calcium hydroxide____
b) KClO3:___potassium chlorate_____
c) NH4OH:___ammonium hydroxide_
d) Fe2(CrO4)3:__iron III chromate__
e) KClO:____potassium hypochlorite_
7-19
Naming Binary Molecular
Compounds
Naming Based on Prefixes:
 Covalently bonded binary molecules are
named using prefixes to designate the
number of atoms in the molecule. The
only exception is that if the first atom in
the molecule has only one atom, the mono
prefix is dropped (understood)
 ex. CO is carbon monoxide
CO2 is carbon dioxide

7-20
Practice
7) Name to following binary molecular compounds
using the prefix system:
a) H20:_____________________________
b) N2O3:____________________________
c) P4O10:___________________________
8) Write the formula for the following binary
molecular compounds:
a) Sulfur dioxide:__________________________
b) Phosphorous pentabromide:________________
c) Carbon tetrachloride:_____________________
7-21
Practice
7) Name to following binary molecular compounds
using the prefix system:
a) H2O:_____dihydrogen monoxide______
b) N2O3:_____dinitrogen trioxide_______
c) P4O10:_tetraphosphorous decaoxide___
8) Write the formula for the following binary
molecular compounds:
a) Sulfur dioxide:_______SO2______________
b) Phosphorous pentabromide:____PBr5_______
c) Carbon tetrachloride:_____CCl4__________
7-22
Acids



Binary Acid: consists of two elements,
usually hydrogen and one of the
halogens.
Oxyacid: contain hydrogen, oxygen and
a third element.
Salt: an ionic compound composed of a
cation and the anion from an acid.
7-23
Oxidation Numbers

Oxidation Numbers: a.k.a. oxidation
states, indicates the general distribution
of electrons among the bonded atoms in
a molecular compound or a polyatomic
ion.
7-24
Oxidation Numbers ~ Rules
1)
2)
3)
4)
5)
6)
7)
8)
9)
Atoms of a pure element have an ox. # of zero
More electroneg. elements in binary molecular compounds
have an ox. # equal to their charge as an anion, the less
electroneg. elements have an ox. # equal to the cation.
Fluorine has an ox. # of -1.
Oxygen has an ox. # of -2 (exceptions are peroxides, -1,
or when bonded Fluorine, +2)
Hydrogen has an ox. # of +1 when bonded with more
electronegative elements, -1 when bonded with metals.
The algebraic sum of the ox. # in a neutral compound is
zero.
The algebraic sum of the ox. # in a polyatomic ion is
equal to the charge of the ion.
Ox. # can be assigned to atoms in ionic compounds.
A monatomic ion has an ox. # equal to the charge of the
ion.
7-25
Oxidation Numbers ~ Examples

What are the oxidation numbers for the
atoms in the following compounds:

H2O: O is -2, H is +1

HNO3: H is +1, O is -2 (x3 = -6), N must
be +5

P4O10: O is -2 (x10 = -20), P must be +5
(x 4 = +20)

ClO3-: O is -2(x3 = -6), Cl must be +5
7-26
Practice
9) What are the oxidation numbers for the
atoms in the following compounds?
a) PCl3:___________________________
b) CF4:_____________________________
c) PbO2:____________________________
_
7-27
Practice
9) What are the oxidation numbers for the
atoms in the following compounds?
a) PCl3 :__ P +3, Cl -1_________
b) CF4:____F -1, C +4___________
c) PbO2 :__Pb +4, O -2__________
7-28
Using Chemical Formulas

Formula Mass: the sum of the atomic
mass of all the atoms represented in the
formula. (this is calculated just like molar
mass, but the units are amu instead of
g/mol)
Ex. What is the formula mass of water?
H2O:
H = 1.01 amu x 2 = 2.02 amu
O = 16.00 amu x 1 = 16.00 amu
Formula Mass of H2O = 18.02 amu
7-29
Practice
11) What is the formula mass of
ammonia?
NH3:
N = 14.01 amu x 1 = 14.01 amu
H = 1.01 amu x 3 = 3.03 amu
Formula Mass of NH3 = 17.04 amu
7-30
Conversions
Mass/Particles using molar mass:
How many formula units are in 29.36g
of NaCl?
29.36g x 6.02 x 1023 units
58.44g NaCl
= 3.024 x 1023 units
7-31
Conversions
Mass/Particles using molar mass:
What is the mass of 5.39 x 1023 molecules
of H2O?
5.39 x 1023 x 18.02 g
molecules 6.02 x 1023 molecules
= 16.1 g water
7-32
Practice
12)
How many atoms of hydrogen are
in 35.67 g of H2O?
13)
What is the mass of 7.89 x 1024
formula units of BaCl2?
7-33
Practice
12)
How many atoms of hydrogen are in
35.67 g of H2O?
35.67g x 6.02 x 1023 molecules x 2 atoms H = 2.383 x 1024
18.02g
molecule
atoms
12)
What is the mass of 7.89 x 1024 formula units of
BaCl2?
13) 7.89 x 1024 units x____208.23 g = 2730 g
6.02 x 1023 units
7-34
Percent Composition

Percent Composition: the percentage by mass of each
element in a compound.
% Comp. = total mass of element x 100
total mass of compound
Ex. What is the % of H and O in one mole of H2O?
% H = 2 x 1.01 g H x 100 = 11.2%
18.02 g H2O
% O = 1 x 16.00 g O x 100 = 88.8%
18.02 g H2O
7-35
Practice
14)
What is the percent comp. of HClO3?
Molar Mass = 84.46 g/mol
%H = 1.01 x 100 = 1.20% H
84.46
%Cl = 35.45 x 100 = 42.0% Cl
84.46
%O = 48.00 x 100 = 56.8% O
84.46
7-36
Empirical Formulas

Empirical Formula: consists of the symbols for
the elements combined in a compound, with
subscripts showing the smallest whole number
ratio of the different atoms in the compound.
Ex. Empirical formula = H2O
Molecular formula = H4O2
= H6O3
7-37
Empirical Formulas
An unknown compound was found to be 75% C and 25% H.
What is the empirical formula?
A 100.0g sample would have 75.0g C and 25.0g H:
75.0 g C x 1.0 mol C = 6.25 mol C atoms
12.01 g C
25.0 g H x 1.0 mol H = 25.0 mol H atoms
1.01 g H
Make a ratio of Moles of each element divided by the smallest
number of moles.
C: 6.25 = 1
6.25
H = 25.0
6.25
= 4
7-38
C:H is 1:4
the compound is
CH4
Empirical Formulas
15)
Now you try one: determine the empirical formula for a
compound containing 7.30 g Na, 5.08 g S and 7.62 g O.
7.30 g Na x 1.0 mol Na = 0.318 mol Na atoms
22.99 g Na
5.08 g S x 1.0 mol S = 0.158 mol S atoms
32.07 g S
7.62 g O x 1.0 mol O = 0.476 mol O
16.00 g O
Na: 0.318 = 2.01
S = 0.158 = 1
0.158
0.158
The compound is Na2SO3
7-39
O = 0.476 = 3.01
0.158
Molecular Formulas
Molecular Formulas give the actual
number of atoms of each element in a
molecular compound. This is always a
whole number multiple of the empirical
formula.
By dividing the molar mass by the empirical
formula mass, you get the molecular
formula.
7-41
Practice
16) Find the molecular formula for a compound that contains
4.90 g N and 11.2 g O with a molar mass of 92.0 g/mol.
4.90 g N x 1.0 mol N = 0.350 mol N
14.01 g N
11.2 g O x 1.0 mol O = 0.700 mol O
16.00 g O
N: 0.350 = 1.00 mol N
0.350
O = 0.700 = 2.00 mol O
0.350
NO2 is the empirical
formula.
Molar mass
= 92.0g/mol = 2
Empirical formula mass
46.01g/mol
Molecular formula = 2 X empirical formula = N2O4
7-42
Ch. 7
The
End!